Abstract
Reaction of tert-butyl trans-lithiopropionate (6) with (S,S)-diisopropylethanediol («DIPED»)(1R)-(1-bromopentyl) boronate (9a) yielded semipurified tert-butyl (2S,3S)-3-hydroxy-2-methylheptanoate (11a) («threo») in a 60:1 ratio to the «erythro» diastereomer. Other threo/erythro ratios included DIPED (1R)-(1-bromo-2-methylpropyl) boronate (9b) to crude 11b, 15:1, DIPED (α-bromobenzyl) boronate (9c) to crude 11c, 8:1; (3S,4S)-2,5-dimethoxy-2,5-dimethyl-3,4-hexanediol (1R)-(1-bromo-pentyl) boronate (9d) to semipurified 11a, 10:1; and pinacol (1-bromopentyl) boronate (5) to semipurified racemic 11a, >100:1. These reactions are sluggish, and α-bromo boronic acid esters generally give better yields than the corresponding chloro compounds
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